A person being transported on a wheeled unit, such as a wheelchair, stroller and tricycle, is dependent upon a caregiver for responsibly directing the wheeled unit to an intended destination. During periods of carelessness or forgetfulness, however, the caregiver at times releases his or her grip on the wheeled unit. The caregiver usually remembers to quickly grasp the wheeled unit once again, but if the wheeled unit is advancing on an inclined surface, the wheeled unit will uncontrollably roll in a descending direction as a result of the momentary release of grip to endanger the person being transported. The person being transported generally is incapable of preventing the uncontrollable rolling condition.
One prior art gravity reactive braking system is mounted on an electric wheelchair, which provides automatic braking. However, the cost of such an automatic braking system is exorbitant.
It would therefore be desirable to provide a gravity reactive braking system for use in conjunction with a manually powered wheeled unit.
Another prior art gravity reactive braking system is disclosed in U.S. Pat. No. 7,316,298. A speed pacer braking assembly includes a downhill activator for selectively engaging a disc brake system when a predetermined incline is reached while descending in a forward direction. The downhill activator comprises a weighted pendulum with a weighted head that pushes against the inner ring of a safety bearing which is integral with the wheel axle when a down slope is encountered to overcome the inner bias of an internal spring and to cause the inner ring to engage an outer ring of the safety bearing. A braking force previously applied to the disc brake is thus communicated to the outer ring by interlocking gear teeth to result in a corresponding change in rotational speed of the axle. An anti-rollback assembly comprises cams which are provided with teeth for interlocking with cooperating teeth of the inner ring of the safety bearing when the wheelchair frame is positioned at an incline, so that rearward rotation of the wheels are prevented in that direction, while freewheeling in forward and rearward directions is permitted when the wheelchair frame is positioned on a level surface as a result of the clearance between the cam teeth which are provided with teeth for interlocking with cooperating teeth of the inner ring teeth.
This prior art gravity reactive braking system is costly due the need of a separate mechanism for both the downhill activator and the anti-rollback assembly, and also due the need of manufacturing precision cut teeth from metallic material to avoid excessive wear as a result of the significant stress to which the teeth are subjected.
Another expensive to manufacture manual wheelchair is disclosed by U.S. Pat. No. 6,805,371, which comprises a two-gear arrangement. The gear assembly includes two spaced cage plates which are joined by fixed shafts having unidirectional rollers positioned thereon around the periphery thereof. The rollers have an exterior surface portion which engages with the interior surface of the gear assembly housing in such a way as to readily permit movement in the forward direction, but to prevent movement in the rear direction, unless the hand rims are used to rotate the housing relative to the gear assembly. The cage plate structure has rubbing elements which interact with the interior surface of the housing to pbaruce an additional braking force for downhill terrain.
It is an object of the present invention to provide an inexpensively manufacturable gravity reactive braking system for a manually powered wheeled unit.
It is an additional object of the present invention to provide a gravity reactive braking system for a manually powered wheeled unit that employs a same mechanism for both a downhill brake assembly and an anti-rollback assembly.
Other objects and advantages of the invention will become apparent as the description proceeds.